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Pseudopalatus (Phytosauria) digital endocast and sensory system in archosaurs



From: Ben Creisler
bcreisler@gmail.com


A paper in the new JVP:

Waymon L. Holloway, Kerin M. Claeson & F. Robin O’Keefe (2013)
A virtual phytosaur endocast and its implications for sensory system
evolution in archosaurs.
Journal of Vertebrate Paleontology 33(4): 848-857
DOI:10.1080/02724634.2013.747532
http://www.tandfonline.com/doi/full/10.1080/02724634.2013.747532#.UcnlL_m1FcQ

Many recent studies have detailed the morphology of archosaurian
endocrania. However, the outgroup to Archosauria, Phytosauria, has yet
to be studied with modern techniques that would allow reconstruction
of their internal anatomy. Pseudopalatus mccauleyi is a derived
phytosaur from the Upper Triassic Chinle Formation, Arizona. A skull
of P. mccauleyi, USNM 15839, was imaged using computed tomography in
order to create the first high-quality, digitally reconstructed
phytosaur endocast. Pseudopalatus mccauleyi exhibits overall endocast
morphology that is similar to that of an extant crocodylian. These
clades, phytosaurs and extant crocodylians, exhibit convergent
Baupläne and similar inferred ecologies. A notable difference between
the endocasts of the two clades is a considerable dural expansion in
P. mccauleyi that denotes a large pineal body. This expansion, and the
overall morphology of the endocast, is consistent with the historic
endocranial reconstructions of the phytosaurs Pseudopalatus buceros,
Smilosuchus gregorii, and Parasuchus hislopi. A comparison with
phylogenetically diverse archosaurian endocasts reveals that endocast
morphologies are highly conserved within Pseudosuchia, regardless of
Bauplan or ecology. This conservatism is in contrast to the diversity
of endocast morphology observed within Theropoda and Sauropodomorpha,
or between members of those clades and Pseudosuchia. The most
pronounced variability in pseudosuchian endocast morphology is a trend
in size reduction of the pineal region, from a large basal condition
to a reduced derived condition wherein the pineal region is
indistinguishable from the rest of the endocast. A similar trend in
pineal reduction is also seen in theropods and sauropods.